Modern Vespa

Ahoy friends,

I'm working on a new friends ET2. It is having ignition problems that i've narrowed down to the main wiring harness.

So far I've,
Replaced the stator/ pickup
Replaced the CDI
Disconnected the kill switch
Disconnected the starter relay
Disconnected the key switch
Disconnected the stator from the main harness.

If I disconnect the main harness from the stator I have consistent strong spark at the plug. If i plug in the harness to the stator I have spark for a few kicks and then nothing.

So far as long as the main harness plug is connected it wont spark, regardless of what else is connected/ disconnected.

The green wire is the ignition/kill wire. I tested it looking for shorts to ground with my multimeter and nothing. Visual inspections came up with no visible chafing. Testing AC voltage at the green wire disconnected from the harness I'm over 60V AC when kicking. As soon as I plug it into the harness I get a spike of 20 and then no AC voltage at the green wire.

So, does anyone have any ideas on how to narrow down where in the harness my problem lies?

I don't know what your exact problem is but if I was looking for an electrical problem I would look for continuity from one end of a wire to the other end. If no continuity I would open up the harness about halfway and check from there to each end. The idea is to narrow down where the problem is.

I hear you about checking for continuity. My green kill wire has good continuity and no shorts to ground. Sadly I havent found a good wiring diagram to trace out wires related to the ignition system so I'm shooting blindly here. Once I do, I'll start checking for continuity/ shorts.

I figured it would be easy to find the problem by testing and then disconnecting one ignition related item at a time until the problem subsided but so far thats not helping.

Do neither of the wiring diagrams on my website help?
https://manuals.wotmeworry.org.uk/Vespa/ET2/

Ha thanks Jim! Of course I missed it. I downloaded the workshop manual Zip file and was going through those.

If you know the the green wire is the ignition/kill switch do the volts go from 0 to 12 or open to closed if you cycle the kill switch? I'm sorry I don't know your bike I'm just thinking out loud here and trying to help.

On first read- this sounds like a possible stator problem to me - however i'm not 100% sure by any means.


but...


here is a link to a stator test procedure for piaggio 2 stroke models - the tests are quite easy to do..... so it may narrow down the problem.....

https://www.pedparts.co.uk/blog/piaggio-ignition-fault-finding

hope this helps.

Fabio-

Thanks for posting that. I found that same link on a previous ET2 thread and used it to test both the original stator and the replacement I bought from Scooterwest. Both stators turned out ok according to those tests IF I disconnect the harness from the stator.

Using Jim's links it looks like 2 wires at the plug go to the regulator (Yellow and gray), one wire to the key switch (green) and the blue wire to the fuse. I'll have to confirm with a meter that this everything's correct and they have continuity, no shorts.

Find all the harness earth points and make sure they are all good. That should include the engine earth etc. Remove them all, clean and replace. Use some dielectric grease or vasalene on them to make sure all is good. Then its worth studying the wiring diagram so you can check each bit for continuity. It's time consuming and may take you a while. But it's really the only way if the stator is ok.

Sorry for the delay. I was away for work.

I cant find the motor ground connection or the wires to the stater motor, but I've disconnected everything else stator related. That includes the key switch, kill switch, starter button relay, starter motor relay regulator and even fuse to the battery.

The new stator checks out exactly as the old one that is since removed.

I verified by kickstarting the scooter with the harness removed and the scooter runs and revs. Connect the harness and the motor dies (even with everything removed).

I started the scooter and using some alligator clips connected the harness connectors except the green kill wire. Everything runs like it should. Moment I connect the green kill wire it dies (again everything is disconnected).

Then I go to test the green kill wire for continuity to ground, nada, nope, zilch, zero. Checked for continuity between the green wire and any other of the 3 wires at the harness connector (yellow, blue, blue/grey) and still nothing.

Bought the $40 ET2 service manual from Scooterwest and it has nothing inciteful. Has a wiring diagram in Italian which I'm slowly comparing to Jim's. So far everything has matched the ET2 later wiring diagram posted on Jim's website.

At a loss now. Going to drink some wine and scratch my head. Anyone got any suggestions?

Ok so I lied and it turns out the service manual diagram was different from Jim's. Still following the hunch about the green wire, I changed grounds and used the negative battery terminal as my grounding point and then started wiggling the green wire. I eventually found the short in the green wire right where it branches off to the key switch.

Rather than split the harness open, I cut the green wire at the harness plug and at the key switch. I was also able to remove every wire from the plastic holder with a small jewelers screwdriver. A little solder and insulation later, I had a lone green wire plugged in and every other wire cleaned and put back where its supposed to be.

Fired it up noticed an oil leak coming out of the belt cover. Quick check and the outlet hose coming from the oil pump was nicked. Fixed that and then went to change the brake fluid. Brake fluid looked like Coca-Cola. New fluid in, plastics on, spin around the block and called the owner. Owner's stoked and out on a test ride at the moment. Hopefully he's happy and this is out of my hair.

Thank you all for your help.